The introduction of Automatic Number Identification (ANI) added a new dimension to emergency call services such as 911. The caller's phone number could now be delivered along with a call and be displayed on a Public Safety Answering Point (PSAP). The method of using ANI can identify the caller even if the caller is not able to do so themselves. ANI is used to help ensure the feasibility of all callbacks in all emergency situations. The PSAP also uses the caller's telephone number to identify the caller's name and address information, as telephone companies store subscriber data based upon telephone number. Also, equipment and corresponding data circuit(s) at the PSAP can take the telephone number, wrap it in a data message, and use it to query an Automatic Location Identification (ALI) database, which has been specifically constructed for this purpose. This configuration facilitates the automatic delivery of the name, address and telephone number, however only for 911 callers having land based phone lines that are installed in a permanent, known, physical location. The telephone numbers of traditional telephones have a constant location associated therewith, since both the telephone number and the telephone location is associated with the installed service jack, due to the topology. This is not the case with more transient telephone devices, such as IP phones and mobile telephones.
Telecommunication rules require mobile phones to provide their latitude and longitude to emergency operators in the event of a 911 call. Carriers can choose whether to implement this via GPS chips in each phone, or via triangulation between cell towers. In addition, the rules can require carriers to connect 911 calls from any mobile phone, regardless of whether that phone is currently active. A mobile caller's geographical information may not always be available to the local PSAP, due to limitations in technology (e.g. of the mobile phone, cell phone towers, and/or PSAP equipment).
Further, if 911 is dialled from a commercial IP telephony service, depending on how the provider handles such calls, the call may not go anywhere at all, or it may go to a non-emergency number at the public safety answering point associated with the billing or service address of the caller. Because a VoIP telephone call can be made using any broadband Internet connection, the IP caller could be many miles away from their home. If the IP call goes to an answering point at all, it could be associated with the caller's address and not the actual location of the IP phone. Further, the use of GPS technologies (as for cell phones) may not always be feasible for IP phones, since they can be installed indoors where a consistent GPS signal may not be obtainable.
Selective routing is important to provide response efficiency for the emergency services responding to the caller. Selective routing routes the 911 call to the proper PSAP, based upon the known location of the caller. Selective Routing can be controlled by the Emergency Service Number (ESN)—a three to five digit number representing a unique combination of emergency service agencies designated to serve a specific range of caller addresses within a particular geographical area or Emergency Service Zone (ESZ). Emergency calls can use a ten-digit ANI number, out pulsed by a PBX/call server, that is combined with the ALI or Emergency Response Location (ERL). For example, the ALI or ERL is a 20-character field that defines the location of a 911 caller including the floor/room/descriptive area within any building. Each phone that can dial 911 should have a location associated with it at the regional ALI database. Current emergency call systems (e.g. enhanced 911 systems) are configured to use selective routing, ANI, ALI, selective transfer and fixed transfer (i.e. speed dialing).
However, updating and maintaining this critical ALI information at the regional database requires strict guidelines and potentially many human resources in a complex environment that is subjected to constant changes. Further, as the IP phone changes locations, the new location of the user must be registered on the communications network in real time. Tracking the location of IP phones can be a significant challenge, as in IP telephony the identity is carried in the phone (i.e. the MAC address is associated with the phone user). Therefore, a problem arises when the IP telephone user changes location, which makes determination of the location of the user placing the 911 difficult to establish. This is due to the fact that all calls are associated with the MAC address of the calling IP telephone, where no tangible information is currently available disclosing the physical location where the call originated.